1. Field of Invention
The invention relates to an antenna and, in particular, to a dual band and broadband flat dipole antenna, which can increase the operation bandwidth of the antenna for applications in more countries or areas.
2. Related Art
The prosperous development of wireless transmission industry has carried out various products and techniques for multi-band transmission, so that many new products have the wireless transmission function so as to meet the consumer's demands.
The antenna, which is used for radiating or receiving the electromagnetic wave, is an important component in the wireless transmission system. The wireless transmission system would not work normally such as radiating or receiving data if it lack of the antenna. Therefore, the antenna is indispensable in the wireless transmission system.
Choosing the suitable antenna not only can be contributive to collocate the appearance of product and to increase transmission characteristics, but also can decrease the production cost. Since the designing method and manufacturing materials are different when designing the antenna for varied application products, and the working frequency band are different in different countries, it is very critical for designing the antenna.
At present, the common specification of frequency band are the IEEE 802.11 and the IEEE 802.15.1 (Bluetooth communication) etc, wherein the Bluetooth communication is worked at frequency band of 2.4 GHz. The 802.11 includes 802.11a and 802.11b standards, which are defined for the frequency band of 5 GHz and 2.4 GHz, respectively.
Referring to FIG. 1, a conventional dual band and dual dipole antenna includes two rectangular radiating metal sheets 11 and 12, and a coaxial line 13. The radiating metal sheets 11 and 12 have corresponding feeding points 111 and 121, and inverted-L splits 112 and 122, respectively. The feeding points 111 and 121 are electrically connected with the coaxial line 13, respectively. The rectangular metal sheets 11 and 12 are divided into a high frequency mode and a low frequency mode by the inverted-L splits 112 and 122, wherein the high frequency mode is from 5.15 GHz to 5.35 GHz, and the low frequency mode is from 2.4 GHz to 2.484 GHz.
However, there has different usable frequency band in different countries, especially to the IEEE 802.11a standard. The component of the antenna must adapt to the range of different bandwidth, and, for example, the output must be a high frequency band (5.47–5:725 GHz), 1 watt to adapt for all country channels in the Europe.
As mentioned above, the conventional dipole antenna only covers a part of the bandwidth, and the dipole antenna for application products, therefore, is unable to be applied in different countries because the available bandwidth is probably restricted in different countries or areas.
It is therefore a subjective of the invention to increase the operation bandwidth of a dipole antenna to adapt to the requirement for more country areas.